Sedimentary Facies And Reservoir Characteristics Of Permian Maokou Formation In East Region Of Sichuan

Maokou Formation of Permian has always been an important horizon for exploration in Sichuan basin.In 2018,well yuanba 7 in northern Sichuan drilled into the platform margin facies zone of Maokou Formation to obtain high-yield industrial gas flow with a daily output of 105.9×10~8m~3,showing great exploration potential of maokou formation.The eastern region of Sichuan is located in the eastern Sichuan basin.except carboniferous system,the exploration degree of other strata is low.the maokou formation has not been systematically studied.does the Maokou Formation in the eastern Sichuan region have a similar platform margin zone in the yuanba region of northern Sichuan?How is its plane spread and whether there are high-quality reservoirs developed?What are the reservoir control factors?These doubts restrict the next exploration constituency of Maokou Formation in East Sichuan.Therefore,this time,under the guidance of multi-disciplines,based on field profile observation,core and thin section identification,combined with logging and seismic data,the division and correlation of Maokou Formation strata in eastern Sichuan are carried out,sedimentary facies division marks are established,sedimentary facies plane distribution characteristics of each layer of Maokou Formation are characterized by combining sedimentary connected well contrast profile and beach specific plane characteristics,reservoir lithology,physical properties,electrical properties,gas-bearing characteristics and their relationships are studied,and reservoir development influencing factors are analyzed from the perspectives of structure,deposition,diagenesis and so on,finally reservoir favorable areas are predicted.This will lay a solid foundation for the next step of oil and gas development.The Maokou Formation in the study area is divided into four sections from bottom to top.Influenced by Dongwu movement,the fourth section of Maokou Formation is almost completely denuded and the third section of Maokou Formation is mostly denuded.Maokou Formation has complex petrological characteristics,mainly developing bioclastic limestone and siliceous rocks,and locally developing porous dolomite,in which bioclastic limestone mostly develops pore fractures.The study area is a rimmed carbonate platform sedimentary model.Four subfacies,namely open platform,platform margin,slope and basin,are developed from south to north in sequence,which is not the whole stable open platform deposit as previously thought.The continuous decline of sea level during the deposition period of Maokou Formation in the south of the study area has a typical facies belt evolution characteristic from deep to shallow.The late stage of Maokou Formation in the middle and north of the study area is affected by the early tensile fault activities of Dongwu Movement,and a multi-stage transgression-regression cycle evolution process occurs.The differential rise and fall make the early stable platform deposition pattern change into the late tensile rift basin pattern.Sedimentary facies belt changes rapidly and the development position of platform margin facies belt is unstable,which is mainly controlled by 15#and 16#deep faults.The basin subfacies developed a set of siliceous mud shale Gufeng section,which is isochronous out-of-phase deep water deposition with Maokou Formation,starting from the second b section of Maokou Formation and ending at the second a section of Maokou Formation.The beach facies deposition of Maokou Formation develops.When the beach ratio is greater than or equal to 0.3,can effectively guide the distribution of beach facies deposition,and the larger the beach ratio is,the higher the beach facies deposition energy is.The difference and distribution range among low energy beach,high energy beach and platform margin beach are defined according to the beach ratio.The reservoir rock type is mainly bioclastic granular limestone,and a small amount of dolomite is developed.Dolomite mostly develops bioclastic beach facies.The types of reservoir space are mainly fracture-cavity type,fracture type and pore-cavity type,which are generally low porosity and low permeability reservoirs,the reservoirs are mainly distributed in the north of the second b section of Maokou Formation,the middle of the second a section of Maokou Formation and the middle and south of the third section of Maokou Formation,The gas-bearing layer shows mainly micro-gas.Reservoir development is mainly affected by sedimentation,structure and dolomitization.According to the superposition effect of sedimentary facies,reservoir space type and reservoir gas-bearing type,four types of favorable reservoir areas are divided in the area,of which type I favorable reservoir areas are developed in the second b section of Maokou Formation,the second a section of Maokou Formation and the third section of Maokou Formation,and all four types of favorable reservoir areas are developed in these three layers.The composition and distribution on the plane of favorable zones of the reservoir have zoning,which reflects the heterogeneity of the reservoir,the connectivity of the reservoir plane and the storage and production capacity of the reservoir.